Variable valve drives have become known in various embodiments in recent years as a means for reducing fuel consumption and emissions. With such variable valve drives, the roller drag lever of the gas exchange valves is no longer actuated directly by the camshaft, but via a working cam contour of an intermediate lever. When the camshaft rotates, this intermediate lever is guided on a contour by a first roller so that a tilting movement of the intermediate lever causes a movement of the working curve contour on the roller of the roller drag lever. The manner in which the working curve acts on this roller drag lever is, however, dependent on the position of a rotatable control shaft that acts on a second roller of the intermediate lever. By changing the position of the control shaft, a varied tilting movement of the working curve contour and thus a varied opening and closing movement of the gas exchange valve are caused.
In order to perform this function with sufficient precision, it is therefore necessary to press the rollers of the intermediate lever both against the slotted guide and against the camshaft and the control shaft for all positions of the camshaft, the slotted guide, and the control shaft. Spring elements are used therefor that are most often double-leg springs with two oppositely wound helixes, the two spring end legs thereof respectively being prestressed to bear on one of the drag levers, while the intermediate leg is fixed, for example, to the component forming slotted guide.
DE 10 2007 047 582 A1 describes a means for controlling the residual gas content of cylinders in an internal combustion engine, wherein a double-leg spring is fastened above the slotted guide path by its intermediate leg, and the helixes of the spring are also arranged above the component supporting the slotted guide. The spring end legs engage the axis of the camshaft rollers and load the camshaft rollers against the camshaft and the slotted guide. In order to additionally provide that the control shaft roller rests on the contact shaft, a secondary spring is fastened at the slotted guide component, the end legs being prestressed to bear against the intermediate lever at the level of the axis of the control shaft roller and to thereby press the roller against the control shaft.
This structure has the disadvantage, however, that two different spring elements must be used to generate sufficient pressing forces. DE 10 2010 048 708 A1 therefore describes a spring arrangement in which only one spring element is used to load the camshaft roller against the slotted guide and the camshaft and to tension the control shaft roller against the control shaft. For this purpose, a spring element is arranged so that it engages the intermediate lever in the region of the working cam and exerts a force in the direction of the contour as well as a force perpendicular thereto. A torque is thereby generated about a fulcrum between the two rollers which causes the control shaft roller to be loaded in one direction toward the control shaft, and the camshaft roller to be loaded in the opposite direction towards the camshaft. A problem with this structure is, however, that a direct pressing force is exerted on the control shaft which, in such a valve drive, is already subjected to high loads and increased wear.